- South Africa's worst-ever earthquake was in the Western Cape, but mining areas have much more to fear.
- The Council for Geoscience is not seeing anything that makes it worried about Cape Town right now.
- Here is how some of South Africa's worst earthquakes played out, from Tulbagh in 1969 to Bela-Bela in 2013.
- For more stories go to www.BusinessInsider.co.za.
South Africa is not a particularly earthquake-prone country – compared to the likes of China, Iran or Japan – but it does have the unique distinction in that the majority of its seismic activity is caused by deep level mining.
More than 80% of seismic events recorded in South Africa are mining related, says David Khoza, executive manager in applied geoscience at the Council for Geoscience (CGS) in Pretoria. Areas that are particularly affected are the deep-level gold mining areas of Orkney, Klerksdorp, and Carletonville in the North West; the gold mining areas around Welkom in the Free State; and the iron ore mining areas of the Northern Cape.
But "you do get natural geological earthquakes that result from tectonic activity along fault lines, such as that which was recently experienced in the Western Cape," says Khoza.
The recent 2.3 magnitude earthquake that occurred roughly 10km north of Durbanville in the Western Cape over the weekend, was one such natural earthquake. The culprit in this case is thought to be a fault line that is part of a network of faults in the Western Cape region.
However, Khoza says, Capetonians have no need to panic.
“Unfortunately, one of the scientific limitations of geoscience is that we cannot predict when an earthquakes will occur but the CGS has a number of seismic instruments which are recording these events on a 24-hr basis,” says Khoza. “For now we are monitoring these events and have not recorded any increased seismicity in the Western Cape that would cause us to worry.”
If anything, South African mining towns have more to be to be concerned about, particularly those in close proximity to deep level gold mining. A seismic hazard map of South Africa produced by the CGS, shows that gold mining towns like Orkney, Klerksdorp, Stilfontein and Carletonville, as well as Welkom in the northern Free State, are far more susceptible to seismic events than the Western Cape.
Nevertheless, the most destructive earthquake to ever occur in South Africa occurred in a small Western Cape town.
Here are South Africa’s worst seismic events in the last century.
South Africa’s most devastating earthquake occurred in the small Western Cape town of Tulbagh at 22:03 on 29 September 1969, caused by a tectonic shift displacement of 26cm over 20km.
It had a magnitude of 6.3 Mw and caused significant damage in Tulbagh as well as nearby Ceres, Wolseley, Porterville, and Worcester. Although the epicentre of the quake was in Saron, near Tulbagh, it was felt as far away as Durban.
It caused 12 deaths, including several children from the Steinthal Kinderhuis, and left many homes and historical buildings uninhabitable. The main shock lasted just 15 seconds but a series of aftershocks continued for six months with the worst occurring on 14 April 1970 with a magnitude of 5.7 Mw.
At 12:22 on 5 August 2014 the small gold mining town of Orkney in the North West was the site of South Africa’s worst earthquake since the Tulbagh event.
It measured 5.5 on the Richter scale and was blamed on heavy mining activity in the area. Tremors were felt as far away as Botswana, Mozambique and Durban.
31-year old Leshomo Makhaola was killed by the quake when a wall of an old house collapsed on him - 34 miners were also trapped underground for a period before being rescued. All were treated for minor injuries, with one also suffering a broken leg.
At around midday on 9 March 2005 an earthquake measuring 5.3 on the Richter scale occurred 2,400 metres below the earth’s surface in the small North West town of Stilfontein.
About 3,200 miners were underground when the first tremors were felt but by 19:00 that evening 3,158 had been brought to safety. The 42 remaining miners were trapped more than 2km below ground at a gold mine operated by DRDGold. Forty were ultimately rescued with half sustaining minor injuries and a further 20 hospitalised with serious head trauma.
Two miners died in what remains one of South Africa’s biggest mine-related seismic events.
The Free State mining town of Welkom suffered a seismic event on 8 December 1976, which measured 5.2 on the Richter scale and left four miners dead.
Although it caused damage to buildings and underground mining infrastructure across the city, the most significant was the collapse of a six-storey block of flats approximately 75 minutes after the quake. Fortunately the building was evacuated before it collapsed.
There is some debate as to what caused the earthquake. At the time Piet Pienaar, who was a consulting geologist for Anglo American, was cited in The Friend newspaper as saying it was the result of geological phenomena and not mining related. However, subsequent papers appear to question this explanation.
At 21:18 on 2 December 2013 the small Limpopo town of Bela-Bela was struck by an earthquake that measured 4.8 on the Richter scale.
Although the epicentre of the quake was about 25km south-east of the town of Bela-Bela, tremors were felt as far away as Randburg and Parkhurst in Johannesburg, Witbank in Mpumalanga and Soshanguve in Pretoria.
Other than reports of walls shaking, no serious injuries or casualties occurred.
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